Convention frames are typically assembled by joining frame members having connection surfaces cut to 45.degree. at both sides to be assembled at right angles to each other, attaching L-shaped corner connection fittings to the connecting parts, fixing them to tile frame member by rivets or set screws and assembling frame members to a square or rectangular frame.
Frame picture units typically comprise a picture assembly of a transparent protecting cover (made of glass or plastic), a mat, a picture and a backing board (in that order from front to back), the outside edges of which are encased in a frame. The most common frames are rectangular or square in plan and typically comprise four framing members joined together with ends mitered at a 45.degree. angle. The framing members may be made of, for example, wood, metal or plastic. When made of wood, the frame members have an outer surface that is typically decoratively shaped or carved, and an inner surface. The inner surface is usually L-shaped in cross-section, comprising a flat front surface which engages the protective cover and a flat side surface. When using wooden framing members, the members are usually glued or nailed together to form the frame. The assembly is placed in the frame with the protective cover engaging the front inner surface, and tacks or other retaining members are driven into the flat inner side surface of each framing member to secure the picture assembly in the frame. While wood has for years been the most common framing material, metal and plastic frames are also in common use. Most metal framing members, like wood framing members, also have mitered ends cut at a 45.degree. angle, however, the means for joining them together is different.